Zeckendarmmikrobiom und -anfälligkeit für Borrelieninfektion

Ixodid ticks (Acari: Ixodidae) are obligate hematophagous ectoparasites that feed on the blood of various terrestrial vertebrates. Their main importance lies in their ability to maintain and transmit a multitude of pathogens of medical and veterinary importance, including Borrelia burgdorferi, the causative agent of Lyme borreliosis. The blood digestion process in the guts of ticks ensures an optimal microenvironment for the survival and maintenance of the tick microbiota, likely composed of bacteria, archaea, fungi, and viruses (Narasimhan and Fikrig, 2015; Bonnet et al., 2017; Cabezas-Cruz et al., 2018). The term ‘microbiota’ refers to all microorganisms that share the tick guts space, while the term ‘microbiome’ refers to the collective genomes of these organisms. Apart from pathogenic microorganisms, ticks also harbour very diverse communities of intra- and extracellular endosymbionts that seem to have an important role in tick biology and in the transmission of tickborne pathogens (Narasimhan and Fikrig, 2015; Bonnet et al., 2017; de la Fuente et al., 2017). A growing body of research suggests that bacteria in tick guts may directly and/or indirectly affect the colonization of specific pathogens within the vector host, providing a new avenue for interrupting pathogen transmission (e.g. Narasimhan et al., 2014, 2017; Abraham et al., 2017). For instance, the gut microbiome of Ixodes scapularis, a major vector of B. burgdorferi in North America, modulates colonization with Borrelia spirochetes (Narasimhan et al., 2014). Specifically, the perturbed gut microbiome significantly increases the engorgement weights of larval ticks, but reduces Borrelia colonization, suggesting that the normal microbiome facilitates B. burgdorferi infection in ticks (Narasimhan et al., 2014). However, further studies are required for a full mechanistic understanding of the complex networks of interaction between non-pathogenic microbial components and B. burgdorferi persistence in the ticks (Kurokawa et al., 2020). Indeed, the extent to which and how the gut microbiome of the Ixodes ricinus tick specifically influences the colonization and transmission of European genospecies of B. burgdorferi, such as Borrelia afzelii, remains poorly known. These findings warrant further investigations of whether manipulation of the tick gut microbiome may influence tick vector competence and susceptibility to Borrelia species. We intend to study the role of gut microbiome of I. ricinus in the infection success of B. afzelii and the mechanisms involved in the complex relationships. Understanding the functional consequences of tick-microbiome interactions and the mechanisms by which certain bacterial components of the native gut microbiome might enable Borrelia spirochetes to infect the tick and the mammalian host is of great interest and could spur new strategies to control both Lyme borreliosis and its tick vector.